Question Detail
Question
In humans, red-green colour blindness is an X-linked recessive trait. If a man and a woman produce a colour-blind son, which of the following must be true? a. The mother carries the allele for colour blindness b. The father is colour-blind c. Neither parent carries the allele for colour blindness d. The father carries the allele for colour blindness
Correct Answer
Option A is the correct answer.
Detailed Explanation
For an X-linked recessive trait, a son inherits his X chromosome from his mother and his Y chromosome from his father. Therefore, if a son is color-blind, he must have received the recessive allele on the X chromosome from his mother. The mother could be a carrier (heterozygous) or affected (homozygous recessive).
Hint
Sons get their only X from mom.